1. Field of the Invention
The present invention relates to a resin membrane having a metallic layer and a method of producing such a membrane. More particularly, it pertains to a hollow fiber membrane and to a method of producing this membrane.
2. Description of the Related Art
Resin membranes formed of porous resin, particularly hollow fiber membranes (hereinafter referred to simply as membranes), have hitherto been widely used for filtering or removing various inclusions in liquids, such as blood, high-purity water, sterilized water, and the drain and condensate of thermal and nuclear power plants. Although such membranes prevent the permeation of bacteria, they themselves do not have bactericidal action; therefore, bacteria which have not been filtered may gradually accumulate and proliferate inside the membranes. Since the membranes are formed of an insulating resin, they tend to be charged electrostatically. When deposits are reversely charged, the adhesive force between the deposits and the membranes increases, thus increasing the frequency of the backwashing of the membranes and decreasing their life. Such a problem may become pronounced, particularly when cladding in the condensate and drain of thermal and nuclear power plants is purified.
To avoid such a drawback, there are a plurality of conventional membranes (disclosed in Japanese Patent Laid-Open Nos. 60-261502, 63-152404 and 64-56106) in which the surfaces of the membranes are coated with metals in order to provide the membranes with bactericidal action or electrical conductivity so that a build-up of an electric charge can be released.
However, when such a conventional membrane is metallized, plating, vacuum-evaporating and sputtering methods are used to simply attach metal to the membrane. It is therefore difficult to form a metallic layer in a sufficient amount on the membrane. At the same time, since bond strength is weak between the membrane and the metallic layer, the metallic layer easily peels off from the membrane. For example, it is possible that when the membrane is bent, the metallic layer will be readily peeled from the bent portion. Moreover, the amount of the metal adhering to the membrane is small. When this problem is considered together with the problem of the metallic layer being peeled off, the conventional membrane is insufficient for improving its bactericidal action and electrical conductivity. Because of a small amount of the metal adhering to the membrane, it is impossible to strengthen the membrane; consequently, there is a limit to the pressure resistance of the membrane.
To improve the efficiency of treatment using a plurality of membranes, the membranes have heretofore been fixed to make them into a module. Such modules are disclosed in Japanese Patent Laid-Open Nos. 59-179108 and 60-28805, and Japanese Utility Model Laid-Open Nos. 61-13556 and 61-178902. In these conventional modules, a plurality of membranes are bundled, and both ends of the membranes are fixed by an adhesive, such as epoxy or urethane resin, thus making the membranes into modules.
However, the wettability of the adhesive with respect to the membranes is poor, especially in olefin-system membranes. When wettability is poor, the membranes are fixed incompletely, thereby making it difficult to form into a module. Even after the module has been constructed, the strength between the adhesive and fixing portions is insufficient. As a result, liquid may undesirably leak in membrane modules, particularly those in which the liquid is passed through the membranes.
The conventional adhesive is mainly a thermosetting type: a main agent and a hardener are mixed uniformly, and in some cases, an inorganic filler may be added for use depending upon the circumstances. The adhesive must, of course, be deaerated and heated while controlling the temperature thereof because of the hardening time being long. Thermal strain may occur due to the gel time being too short or self-heating. It is thus difficult to control the adhesive which lacks in workability.